A multiple access very small aperture terminal (VSAT) is a satellite ground terminal for a satellite network. A VSAT can perform Internet communication through the satellite network, which uses a star topology in which a subscriber base of remote user terminals all communicate by way of a centralized hub. The hub is used as a gateway that a VSAT goes through to access all other terminals. The hub maintains a master time reference so that the transmissions of all remote user terminals can be synchronized in a non-interfering manner.
A mesh topology is a network arrangement in which remote user terminals transmit a signal directly to another user terminal, via the satellite, in a way that does not require the signal to first be received by a centralized hub. Accordingly, in a mesh network, a VSAT may not have access to the master time reference maintained in the hub. The multiple access nature of VSAT requires synchronized and non-interfering transmission.
In particular, the time synchronization process in a star topology VSAT network uses time-division multiple access (TDMA) for interaction between remote terminals and the centralized hub (transmitters and receiver). The master time reference that is maintained at the hub is broadcast to the remote terminals. Since each remote terminal is located at a different distance (and therefore time delay) from the hub than any other, it must time it's transmissions differently than other remote terminals to ensure its transmissions arrive at the hub without interfering with any other remote terminal's transmissions. As such, the master time reference is synchronized to have a unique solution at each remote terminal. That is, the hub interacts with each remote terminal so that each remote terminal can determine its own unique solution. Each terminal determines its unique solution by obtaining a “copy” of the hub master time reference and offsetting the copy by the time it takes to transmit a signal from the remote terminal to the hub.
There are situations where it would be beneficial for remote terminals that are configured to communicate in a star VSAT network to conduct direct communications without going through the hub. For example, off shore drilling sites with latency sensitive applications like Voice over IP (VoIP) running among those sites may prefer to directly communicate with each other instead of relaying their transmissions through a hub. In such case, the remote terminals configured for a star VSAT network would require a capability to operate both as star and mesh remote user terminals.
The foregoing “Background” description is for the purpose of generally presenting the context of the disclosure. Work of the inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.